I ought to have got much more of a kick out of 'The Purge: Anarchy' than I did, but it lost out by failing to find a voice.

It's the low budget sequel to a low budget movie, last year's 'The Purge', expanding the $3m budget of the latter to $9m. Each has earned over $80m already, meaning that the likelihood of a third, even more ambitious, film in the series is very strong indeed. The way this one ended, with a particularly effective final scene, could easily lead into that third film, even as it wraps up both this one and its predecessor.

It's genre film through and through, a modern take on the sort of outrageous but always legal future that we've seen many times before in cult films. It aims a lot higher than its budget and it succeeds at a great deal, but it falls short of each of the titles it resembles. It doesn't have the wildness of 'Death Race 2000', the stars of 'Escape from New York', the action of 'District B13', the detail of 'Demolition Man' or the Japanese schoolgirls of 'Battle Royale'.

In the end, the closest comparison is perhaps to 'They Live', because it aims to haul this type of cult film into the generation of the 99% and it copies quite a lot from John Carpenter's tale of immoral yuppies as aliens feeding on the poor as they turn this world into their own. Aiming at social comment does give it some effective setpieces, but it falls short because it can't conjure up its own sense of style, something to make it stick in the memory and resonate.

The closest it gets is with its basic concept, that in a future that looks stunningly like the present, the New Founding Fathers have taken control of the United States and implemented the Purge, a annual twelve hour cessation of all laws and emergency services. Their stated goal is to allow the public one day a year to purge themselves of their criminal tendencies, something that has helped reduce crime, unemployment, homelessness, you name it. Society is doing very well under the Purge, it seems, at least on paper.

Unofficially, it achieves this by taking out the poor and needy, something that is being helped along in secret. If you can't find a way to succeed during the year, the annual Purge will sweep you off whatever statistics you're showing up on with extreme vengeance and you won't be anyone else's problem again. If the freaks who turn out for this event don't do it, then the powers that be will find a way to do it themselves. At least, this is the theory expounded by Carmelo, an activist who's been hacking into official feeds to send out his message.

Given that most films would have focused so deeply on the idea that they would have failed to tell a real story, it's ironic that the biggest mistake of James DeMonaco, who wrote and directed, seems to be to lose focus on this concept in favour of a host of little stories. This approach helps him build sympathy for characters who find themselves stuck on the streets during the Purge against their will and it certainly helps him build an agreeable sense of tension, echoing 'The Warriors' in their run for freedom through the big city with enemies all around them. However, it loses the depth it needs to become another 'They Live' in an attempt to be another 'Assault on Precinct 13'.

If DeMonaco fails to provide a strong big picture, he does well with the little stories.

His characters are worth following, even if they fail to stick in the mind. The leader of this motley band is Leo, though I'm not sure we ever hear his name. He's on a quest for revenge, heavily armed and with a powerful armoured vehicle. Not a regular Purger, his conscience forces him to step in to save a couple of ladies, a waitress called Eva and her daughter Cali, perhaps in some sort of attempt to keep on him on the side of good. Finding refuge in his car while he does this are Shane and Liz, a young couple whose car is sabotaged, leaving them stranded in the open during the Purge.

Each of them has depth. Leo is the grounding of the picture, a tough man driven to violence on a day that encourages it, but otherwise a kind man whose sense of decency refuses to be overwhelmed by the opportunity to right his wrong. Shane and Liz are weaker people whose relationship was floundering before the Purge, but who find strength within it to move forward. Eva and Cali are the epitome of the people plagued by this so-called solution: a good and working family struggling to pay for the medicine needed by Eva's sick father. The Purge proves to be a boon and a curse for them in a number of ways.

In spending time to give us strong characters on the side of good, DeMonaco has trouble giving balance to the side of bad. He certainly fills the Purge with a wealth of freaks, but none of them really get to seize their moments. There are snipers on roofs, hunters with dogs, truckers with machine guns, heavily armed gangs in school buses, men on foot with flamethrowers. None resonate. Those that do are kept anonymous behind the easy mask of the wealthy, so can't shine as individuals. Only the lady who hosts an auction to pick victims from the poor for the rich to hunt has a face that stands out, but I couldn't tell you the name of her character.

This is very much a sci-fi dystopia for the 99%. There isn't a single rich person in this film with an ounce of decency. They aren't even merely bad, they're stereotypically evil. The rich in this film aren't hiding at home, boarded up in their mansions, with hired killers protecting their doors. They're paying big money to have poor people delivered to their houses for them to slaughter with machetes in rooms that could have been outfitted by Dexter. At least 'They Live' used aliens for this purpose and never suggested such a polarisation between classes; in avoiding analogy and excluding exceptions, 'The Purge: Anarchy' becomes mere propaganda.

Another problem is that it does well with details, peppering the story with traps in the street, bugs to aid hunters and willing martyrs who commit suicide by Purge, but fails to scale that up to the big picture. How can crime be outlawed but weapons above class whatever be banned? How does the insurance industry treat the day? How long does it take up after each year's Purging? So many questions are raised here that go relentlessly unanswered, but none more so than the behaviour of the Purgers.

Those who flock to the streets to let loose their criminal aggression for twelve hours are the most well behaved bad guys I've ever seen. While everyone seems happy to murder, at least one character descends to attempted rape and some take out very personal vengeances, not one breaks into a store, fires a rocket into a big building or sets fire to anything. Where are all the idealists, the terrorists, those with a grudge against the powers that be? If this was a real 99% story, the banks would be ashes by morning.

What it does is capable, but 'The Purge: Anarchy' aims at far more than it's able to reach. It entertains and, at points, impresses, but it's unable to define itself strongly enough to remain in mind. It starts to fade from the memory during the end credits. By the time the eventual third movie comes out, you'll have to go back to the first two to remind you what they were all about.